1. Field of the Invention
The present invention relates to a sample holder permitting a sample to be observed and inspected using an electron beam or ion beam at high resolution in a case where the sample contains moisture or another liquid component. The present invention also relates to a method of observation and inspection using the sample holder. Furthermore, the present invention relates to an observation and inspection apparatus using the sample holder.
2. Description of Related Art
In a sample inspection apparatus having the configuration of a scanning electron microscope (SEM), a sample to be observed or inspected is placed in a sample chamber whose pressure is reduced by vacuum pumping. Under this condition, the sample is irradiated with an electron beam. As a result, secondary signals, such as backscattered electrons and secondary electrons, are emitted from the sample. These secondary signals are detected.
Similarly, in a sample observation apparatus or sample inspection apparatus having the configuration of a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), a sample to be observed or inspected is placed in a sample chamber whose pressure is reduced by vacuum pumping. In TEM or STEM, the sample placed in a sample chamber is irradiated with an electron beam. The electron beam transmitted through the sample is detected.
In observing or inspecting a sample using such an apparatus, the sample is exposed to a reduced-pressure ambient within a sample chamber. Accordingly, when a sample containing moisture is to be observed or inspected, if the sample is placed intact within the specimen chamber that is a reduced-pressure ambient, water evaporates from the sample. This hinders observation or inspection of the sample under the condition where it contains moisture.
One example of a method of observing or inspecting a sample using SEM without exposing a sample to a reduced-pressure ambient in this way is shown in JP-A-2007-292702 (Application No. 2006-123711) and JP-A-2007-294365 (Application No. 2006-123712). In particular, the inside of a sample chamber is divided into an atmospheric-pressure ambient and a vacuum ambient using a film that transmits an electron beam but does not transmit gas. The sample is placed in the atmospheric-pressure ambient.
In this method, when an observation or inspection is performed, the sample placed in the atmospheric-pressure ambient is irradiated with an electron beam from the vacuum ambient, the beam impinging on the sample via the film. Backscattered electrons are produced from the irradiated sample. The backscattered electrons pass through the film and are detected by a backscattered electron detector mounted in the vacuum ambient. Consequently, a SEM image is obtained.
Another method is described in JP-A-47-24961 and JP-A-6-318445. In this method, a cell structure (sample holder) having a pair of films through which an electron beam is transmitted is placed in a TEM sample chamber. A sample is placed in the cell structure and irradiated with an electron beam. The electron beam transmitted through the sample is detected.
Where a conventional SEM sample holder as described in JP-A-2007-292702 (Application No. 2006-123711) and JP-A-2007-294365 (Application No. 2006-123712) is used, a thin film is used to observe or inspect a sample containing liquid. The thickness of the film is more than 10 nm and so it is difficult to use secondary electrons in imaging the sample. Consequently, backscattered electrons are used for imaging. Hence, it has been impossible to improve the resolution.
On the other hand, the conventional TEM sample holder has used carbon films and mesh. In this case, if the sample is placed in an environment that has been pumped down to some extent, good results will be obtained. However, it has been difficult to obtain 1 atm. pressure resistance. Furthermore, the sample holder is assembled fully manually, requiring much labor. Hence, it is impossible to cope with a large number of samples. Because the sample holder is assembled manually, it is difficult to reduce the spacing between the carbon films. As a result, there arises the problem that the resolution is deteriorated.
The problem common to SEM and TEM is that a sample of more than 1 milliliter is required when the sample is passed through a filter or a medicine is mixed into the sample.